Legacy unsupported variable 'SPLIT_DB' detected

[abreuma677]

I'm trying to clean up my docker definition file. This is the last warning I'm working on. I'm backing up a single MariaDB instance (all databases in it). I have no other DBnn variables set, but the only SPLIT variables I see are for the DBnn parameters. I don't see a DEFAULT parameter for SPLIT in the docs, so I'm a bit puzzled on how to update SPLIT_DB. Can someone give me a suggestion?